Airbag safety systems are well known and widely used in the automotive industry. The basic idea behind inflatable airbags installed in motor vehicles is to serve as a cushioning means for the passenger's head and torso which is thrust forward in the event of a head-on collision. When a head-on collision occurs, collision sensors such as metal distortion sensors activate the airbag inflation device, and the airbag is instantly inflated. Momentum of forward travel causes the head and chest of the passengers sitting in front of the inflated airbag to thrust forward and hit the inflated airbag, which is equipped with air vents. Upon impact of the head and chest with the airbag, air is released from the airbag through the vents thus reducing dramatically the severity of the impact, avoiding head injury inflicted by the windshield, and diminishing whiplash effects.
Recent studies have been carried out on the feasability of implementing airbag safety systems in aircraft. The development of airbag technology for aircraft, including overviews of military helicopter cockpit and commercial transport aircraft and airbag development programs, were discussed in the International Conference on Cabin Safety Research, held in Atlantic City, N.J., on Nov. 14-16, 1995. Projected effectiveness of airbag supplemental restraint systems in U.S. Army helicopter cockpits was discussed in the American Helicopter Society (AHS) annual forum in Washington, DC, on May 11-13, 1994, in Alexandria, Va. This study reviewed army helicopter accident records over a nine year period and developed a computer model to determine the number of fatal and disabling injuries to cockpit crew members that could be prevented with an airbag supplemental restraint system installed inside the cockpit.
In Israeli Patent Application No. 120,334, a multi directional airbag protection device for crews in military combat vehicles was disclosed. That device was designed to provide a restraining means for crew members when the vehicle is subjected to an explosion or a direct hit, in an attempt to prevent, or at least reduce, the number of casualties resulting from the explosion or hit. Upon the deployment of the airbag of that invention, the passenger is instantaneously restrained and tightened to his seat by the airbag.
When an aircraft, and in particular when a helicopter is considered, the severity of an accidental event is much greater than the event of a typical automotive traffic accident, as it involves a vertical drop which increases immensely the energy release upon the impact on the ground, and is therefore generally lethal for the aircraft crew members.
When engine failure occurs in an airplane, aerodynamic structure can provide for a safe landing as the airplane is capable of gliding fairly safely and perform an emergency landing. A helicopter, on the other hand, depends solely on the lift power provided by the rotor blades. This means that if the rotor blades are removed or damaged, the helicopter fuselage is bound to fall freely, subjected to the gravitational force only, and consequently hit the ground at a high energy impact, resulting in the loss of life of most, if not all, of the crew members.
However, if the helicopter engine fails, and yet the rotor blades remain intact, the pilot can still attempt to maneuver the aircraft to a safe landing, with the help of the auto rotation effect. Auto rotation is attributed to the design of the rotor blades, making it possible to keep the rotor blades rotating even when the engine stops functioning. When auto rotation takes place, the aircraft vertical velocity is greatly reduced, bringing the aircraft velocity upon hitting the ground to the order of about 10 meters per second. As a result, auto rotation provides lift power to the aircraft, enough to enable the power to the aircraft and permit the pilot to land the helicopter relatively safely. Helicopter pilots who practice emergency situations are taught to take advantage of the auto rotation effect.
There are different types of helicopters, ranging from very light civilian choppers, up to heavy cargo and troop carrier helicopters, like Sikorsky CH-53. Some helicopters, mainly military ones, have been especially designed to acquire crash resistant structure, like the Apache or the Blackhawk. Yet most helicopter crashes result in very high fatality statistics despite safety equipment.
Investigations of a military helicopter collision accident involving two helicopters in 1997 concluded that one of the helicopters was seen experiencing some yawing, trying to maneuver into landing, before finally hitting the ground and crashing. In Japanese Patent Application No. 7-6328 of Ohtuka Ayako a safety system for helicopters was disclosed. According to this invention, the helicopter is equipped with shafted spare engines, capable of exchanging propellant force in a vertical or a horizontal direction, and inflatable airbags are placed under the body, which can quickly be inflated in case of an emergency forced landing in order to relieve the landing shock. This invention, however, requires the presence of an additional spare engine on the helicopter, which means putting an additional weight on the helicopter and requiring design adjustments, and also relying on the spare engines to operate together with the airbag device. Another problem in Ayako's invention is the possible rebound off the ground the helicopter is likely to experience if the airbag remains fully inflated and does not burst or deflate upon hitting the ground. On the other hand, if the airbag bursts upon impact, it's cushioning properties may be lost, subjecting the helicopter to more energetic impact than configured. It should be emphasized that Ayako's invention provides an airbag protection system designed to be operated by the helicopter's pilot while still in control of the aircraft when there is still some time for the pilot to perform the operations required for the system to work properly, i.e., to engage the spare engines, activate the inflation of the airbags, and adjust the airbag positions underneath the aircraft, before performing an emergency forced landing. The pilot in Ayako's invention uses the spare engines as a temporary replacement for the rotor blades, and the airbag acts merely as an additional means of protection. However, the system described by Ayako will not provide the desired protection in the event of the aircraft dropping unexpectedly and hitting the ground before the pilot could perform all the above actions.
It was found that the human chest can withstand accelerations in the magnitude of up to 40 g and the head can withstand alterations of up to 60 g. However, the spinal column is more vulnerable. In helicopter crashes, it was suggested that in order to mitigate about 80% of injuries in survivable crashes, the peak spinal accelerations should preferably not exceed the order of 10 g. In order to protect crew members of a crashed helicopter, it should be designed not to exceed said accelerations in the form of a safety system installed which would cushion and soften the helicopter crash on the ground, and in particular protect the fuel tanks, as it is vulnerable to explode and burn upon impact with the ground.
It is therefore an object of the present invention to provide an airbag protection system for helicopters, to improve the crash resistance of helicopters.
It is another object of the present invention to provide such a system that would provide helicopters protection in an event of an unexpected drop.
It is yet another object of the present invention to provide an airbag protection system for helicopters that would prevent possible rebound on impact and yet preserve its cushioning properties.